1. Field of the Invention
The present invention relates generally to remote concentration measurement of gases and vapors and more specifically to a remote active vapor concentration measurement system and method thereof in which a range finder is integrated with a remote vapor detection system to permit the measurement of the concentrations of vapors or gases. Such a system allows an accurate assessment of the danger of explosion or toxicity to humans or animals. A remote vapor detection system that may be used in conjunction with the range finder of the present invention is disclosed in co-pending patent application Ser. No. 07/844,524, filed on Mar. 2, 1992 in the name of Maurice Fee, a co-inventor of the present invention.
2. Prior Art
U.S. Pat. No. 4,529,317 to Cramp is directed to a method of monitoring gaseous pollutants. Using laser scanning apparatus, two intersecting scanning beams, coordinated by a central control unit, provide the information necessary to determine the concentration of a known pollutant. Two helium-neon lasers provide a detection beam and a non-absorbed reference beam at a nearby wavelength. The detection and reference beams are passed through choppers and to power meters. Power meters continuously monitor the power output of the lasers. The radiation is detected by a detector and the information furnished to a computer as the central control unit. With this information, the position and/or concentration of the particular pollutant can be determined.
U.S. Pat. No. 3,843,258 to Shupe is directed to a dual beam absorption spectrometer useful for determining the concentration of atmospheric pollutants. The figure illustrates the dual beam absorption spectrometer having signal generating apparatus for providing two coherent wave energy signals, namely, laser signals. Measuring apparatus is provided to receive and measure the intensities of the signals provided after they have traversed a sample containing region. A first signal has a wavelength slightly offset from a second signal so that it will not be absorbed by the predetermined material. In operation, a spectrometer can be used as a field instrument to measure the concentration of a predetermined material along paths of several thousand feet, or several miles.
U.S. Pat. No. 4,496,839 to Bernstein et al is directed to a system for identification of chemical species by laser initiated infrared spectroscopy. The laser is directed at a chemical mass which absorbs energy at the laser wavelength and the absorbed laser energy is re-emitted giving rise to a non-resonant infrared emission spectrum of the chemical species. The identity, as well as its range and concentration, may be established by comparison of its spectrum to that for known species. The system is diagrammed in FIG. 1 of Bernstein et al, showing a CO.sub.2 infrared laser passed through a suitable optic system to the unknown chemical species. The returning radiation is separated by a monochromator into three wavelengths which are then sensed by detectors. The outputs of detectors are delivered to a data acquisition circuit which compares the intensity of the collected radiations from which the identity and concentrations may be determined.
U.S. Pat. No. 4,489,239 to Grant et al is directed to a portable remote laser sensor for methane leak detection. This system is capable of detection of methane and for further determination of concentration thereof. This invention includes a pair of helium-neon gas lasers operating continuously at two wavelengths. The two laser beams are chopped and are directed at the area in which gas detection is to occur. The laser radiation is collected and passed to the optical detector. The detector measures the difference between the two signals and the methane concentration is measured using the differential absorption Lidar technique.
Accordingly, it will be seen that the most relevant prior art known to the applicant includes a patent which requires two specific laser wavelengths to detect the gas of interest and two sites of displaced lasers and receivers. It also includes a patent in which a two specific laser wavelength system only provides average concentration along the total path length. Another particular prior art patent uses a high power laser pulse to excite the specie of interest and measure the wavelengths of the re-emitted radiation for specific identification. By timing between the excitation pulse and a re-emitted pulse, the range is determined. The claim to concentration measurement is based on the return signal from an unknown, compared to the signal from a known quantity. This type of concentration measurement would have to be an average type over some path with large uncertainties. The remaining patents described above, all provide average concentrations over a path length. Using these devices, one could be in an apparent safe area, based on an average measurement of path length, where as the local concentration might actually be lethal. The only two types of systems that provide specific and not path average concentration measurements, are the differential absorption systems using back-scatter from the atmospheric constituents and a system that uses two displaced laser/receiver systems.
There is therefore an ongoing need for a remote active vapor concentration measurement system which overcomes the aforementioned deficiencies of the prior art.